The textural changes (generically referred to as “softening”) that accompany ripening of fleshy fruits are critical determinants of quality and are thus of great commercial importance. Loss of firmness is a major factor limiting transportation and storage of fleshy fruits and it is also associated with the onset of postharvest disease, due to microbial pathogens that penetrate and destroy the fruit flesh. Postharvest fruit quality is dependent on both textural durability during storage and the nutritional and sensory components. The practice of harvesting many fruit prior to full maturity to improve resistance to damage during handling has resulted in crops that typically fail to accumulate a full complement of nutritional compounds, which are essential for optimal quality. Therefore, if the molecular basis of softening could be better understood, and if softening could be uncoupled from other ripening-related processes, fruit could be harvested at a later stage. This in turn would not only make the fruit more resistant to over-softening and less susceptible to microbial infection, but would also dramatically enhance flavor and nutritional content and thus increase commercial value.
A number of tomato ripening mutants have been identified, including rin (ripening inhibitor), nor (non-ripening), alc (alcobaça), and Cnr (Colorless non-ripening), which are impaired in many ripening-related processes and exhibit delayed or impaired softening (Kopeliovitch et al., “Physiology of the Tomato Mutant Alcobaca,” Physiol. Plant. 48:307-311 (1980); Giovannoni, “Genetic Regulation of Fruit Development and Ripening,” Plant Cell 16:S170-S180 (2004); U.S. Pat. No. 6,762,347 to Giovannoni et al.; and Manning et al., “A Naturally Occurring Epigenetic Mutation in a Gene Encoding an SBP-box Transcription Factor Inhibits Tomato Fruit Ripening,” Nature Genetics 38:948-952 (2006)). These mutants have provided insights into several specific aspects of ripening-related metabolism, but their effects on ripening are pleiotropic and some desirable aspects of ripening physiology are adversely affected, which limits their commercial application. For example, the rin mutation, which has been introgressed into a large number of commercial tomato cultivars, slows the rate and/or extent of fruit deterioration, but often has a deleterious effect on color, flavor, and aroma. In this regard, a more desirable tomato cultivar would be one that has reduced or delayed softening, but that exhibits otherwise “normal” ripening, with the attending quality metrics.
The present invention is directed to overcoming these and other deficiencies in the art.